Current practice for ensuring a safe environment for the insertion of a personal computer (PC) card in systems that share common interface signals is by use of mechanical means, such as a push-button switch, to provide an advanced warning of the PC card insertion. The advanced notice halts operations in the host system in an orderly fashion so as to preserve data and operating instruction integrity and to ensure an electrically safe environment for the PC card insertion. This method is unreliable because it depends on a system user to activate the mechanical means before inserting the card.
Another existing method requires connecting a pull-up resistor to one of the backplane socket connector's ground pins which mates with ground pins on the PC card but is not connected to the host system ground plane. If the power and ground pins of a socket are longer than the signal pins, contact of such a pin with socket pin having a pull-up resistor connected to it will cause that socket pin to be high and then go low at the onset of an insertion before any of the signal pins make contact. This provides an advanced indication that a PC card is being inserted. The advanced indication may be used by the host system to indicate any action that might be required for maintaining an orderly system.
The drawback to this second method is that a pin normally used for a ground pin is assigned to insertion detection and thus cannot be used for a normal ground connection between the system and the PC card, resulting in reduced reliability of the PC card interface.
A further disadvantage of this second method is that only one pin is used for detecting the onset of a card insertion. As a result, if the PC card were to be inserted at an angle offset from normal to the socket, contacts at one end of the PC card may make contact before the onset of a PC card insertion can be detected.